* fork.cc (fork_child): Call the __pthread_atforkchild function.

(fork_parent): Call the __pthread_atforkparent function.
* cygwin.din: Export pthread_atfork.
* thread.h (callback): New class.
(MTinterface): Use it.
* thread.cc (__pthread_atforkprepare): New function.
(__pthread_atforkparent): New function.
(__pthread_atforkchild): New function.
(__pthread_atfork): New function.
* pthread.cc (pthread_atfork): New function.

winsup/cygwin/pthread.cc

@@ -29,6 +29,12 @@ pthread_once (pthread_once_t * once_control, void (*init_routine) (void))
   return __pthread_once (once_control, init_routine);
 }
 
+int
+pthread_atfork(void (*prepare)(void), void (*parent)(void), void (*child)(void))
+{
+  return __pthread_atfork(prepare, parent, child);
+}
+
 int
 pthread_attr_init (pthread_attr_t * attr)
 {